sign_android_image: calculate and store the vb meta digest For verified boot, one of the boot parameters is the vb meta digest. The vb meta digest will be set to the hash of the hashes of the system and vendor images. The hash will be calculated and stored in a file in the same directory as the images. Later, the file will be read to retrieve the value for vb meta digest. ARC Keymint CL: https://crrev.com/c/5809618 BUG=b:350826304 TEST=./sign_android_unittests.sh TEST=manually compare arcvm_vbmeta_digest.sha256 and sha256sum output on dut with locally signed image BRANCH=none Change-Id: Icab0a5002a6b0f6537c75b5124587b0a92270f26 Signed-off-by: Luzanne Batoon <[email protected]> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/5826996 Reviewed-by: Vaibhav Raheja <[email protected]> Reviewed-by: Julius Werner <[email protected]>